Process of vulcanizing elastomers



Patented Nov. 29, 1 949 raocass F VULCANIZING ELASTOMERS Bernard M. Sturgis, Pitman, N. J and Arthur A. Baum, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 6, 1946,

Serial N0.'688,691

6 Claims.

This invention relates to an improvement in the process of vulcanizing elastomers. The invention relates more particularly to an improvement in the process of vulcanizing sulfur vulcanizable elastomers by incorporating into the elastomer to be vulcanized a trichloromethyl aryl compound which operates as an accelerator activator and which materially accelerates the vulcanization of the sulfur vulcanizable elastomers in the presence of the usual accelerators.

The sulfur vulcanizable elastomers with which the present invention is particularly concerned are natural rubber, and the butadiene copolymer rubbers which have come into quite general use in place of natural rubber. The term butadiene copolymer rubbers is used to refer to those polymers having rubber-like properties which are produced by the copolymerization of butadiene with one or more copolymerizable vinyl compounds such as styrene or acrylonitrile, the butadiene being present in the mixture to the extent of from 50% to 98% of the total polymerizable material. The butadiene-styrene copolymer rubbers are manufactured commercially under such names as GR-S, GR-S-lO, GR-S-25, GR-S-50 and the like which are the designations given to this type of rubber by the U. S. Government, while the butadiene-acrylonitrile copolymer rubbers are manufactured under such names as Buna N, Hycar OR, Perbunan and Chemig The vulcanization of rubber and the butadiene copolymer rubbers is usually carried out by heating them with sulfur in the presence of certain accelerators. In many cases it has been found advantageous to use other compounds in conjunction with the accelerators which activate the cure obtained with the primary accelerator. These compounds are generally referred to as secondary accelerators or as accelerator activators. While, as their name implies, these activators are often accelerators in their own right, when used in conjunction with primary accelerators they give results not obtainable with either compound when used separately in the sulfur vulcanization of elastomers.

It is an object of the present invention to provide an improved process for vulcanizing sulfur vulcanizable elastomers such as rubber and butadiene copolymer rubbers. A further object of the invention is to provide an improved process for vulcanizing sulfur vulcanizable elastomers in which smaller amounts of the normal vulcanization accelerator may be employed, yet which will give rapid cures and which will produce vulcanized elastomers having improved properties.

We have found that vulcanization of rubber H and sulfur vulcanizable rubber-like materials,,-==

such as the butadiene copolymer rubbers, can be materially accelerated by employing with the sulfur and the usual vulcanization accelerator a trichloromethyl aryl compound in which the aryl radical is of the benzene or naphthalene series and which have the general formula:

R-CCls vators are characterized by their great versatility,

. ene copolymer rubbers.

By the use of these new activators, a large proportion of the relatively expensive rubber accelerators can be replaced by a much cheaper activator. Thus, the cost of acceleration in many formulations can be considerably reduced.

In many cases, the use of trichloromethyl aromatic compounds as accelerator activators results in vulcanizates having appreciably higher tensile strengths. With some elastomers attempts to improve the heat resistance of the vulcanizates, by using low sulfur and high accelerator ratios, result in vulcanizates having lower tensile strength than a stock containing the usual sulfur to accelerator ratio. However, by using the activators of the present invention, low sulfur stocks are obtainable which have excellent tensile strengths.

In Example 1, the effect of o-chloro-benzotri chloride as an activator for various classes of accelerators in natural rubber is shown.

EXAMPLE 1 cured and tested by standard procedure.

I this table, M300 and Mann, refer to the stress in Table I Stock A B C Smoked Sheets Medium processing carbon black Zinc oxide Mereaptobenzoth1azo1e Z-Mereaptothiazoline Tetramethylthiuram monosulfide Butyraldehyde-aniline condensation producto-Chlorobenzotrichloride Minutes I Stock Cure at A B C i D E F G H 15 225 575 125 200 550 550 150 575 M100 30 400 525 225 425 575 800 275 50 575 v 350- 5 375 550 575 800 525 750 1, 775 425 775 1, 975 2,125 525 1, 325 Mm; 1, 250 2, 050 350 1, 425 1, 975 2, 550 1, 025 1,550 2,750 1,150 1,975 1,575 2, 275. 1, 500- 15 2,200 3,075 1,400 2,250 4,500. 4, 750 1,975 5,050 T1; 30 3,075 4,400 2,225 3,025 3,950 4,425 2,850 50- 3,425 4,300 2,750 4,125 3,125 3,875 3,575 15 750 550 770 770 740 720 755 790 E a 30 730 720 740 750 590 680 740 50 680 720 720 680 579 550 720 In. the case of the butyraldehyd'e-aniline conas the vulcanizable elastomer Perbunan (a dens'ation product, the action of the activator copolymer of butadiene and acrylonitrile con- Was so vigorous as to cause reversion on the taining approximately 27% of combined acrylolonger cures, indicating that much shorter time nitrile). Results of these runs are shown in may be employed in effecting. proper curing of Table II.

Table II Stock I I J K L M N 0 P Perbunan 100 100 100 100 100 100 100 100 Medium processing carbon black 50 50 50 50 Zinc oxi e 5 5 5 Stearie acids- 1 Sulfur; I, 1.5 Mcrcaptobenzothiazole 01.4 2-Mercaptothiaz0line Tetramethyl thiuram monosulfide Butyraldehyde'aniline condensation product 0-Ohlorobenzotrichlorider Minutes Stock Cure at. I J K L M N O P 30 525 1, 225 225 925 950 850 200 475 Mm 650 1, 925 375 1, 575 1, 025 l, 420 375 825 750 525 l, 800 1, 025 1, 550 500 l, 225 30 950 2, 400 350 1, 675 l. l, 725 375 925 Mm 60, 1,275 625 2, 2, 950 675 2, 125 90 1, 425 900 000 975 2, 500 1 30 2; 550 3, 000 625 2, 525 l, 775 2, 650 1, 100 3, 100 TB.- ll 60 2, 525 1, 675 1, 300 1, 925 2, 475 2, 950 1, 950 3, 825 90 3, 475 1, 800 1, 775 2, 700 l, 750 5, 050 2, 425 3, 250 30 560 3 625 380 280 690 615 E3 60 440 520 245 325 300 590 430 necessary and effective activation may be obtained with smaller amounts.

The process of Example: 1 was repeated, using In certain of the above runs, the eiiectof theactivator was so great that the resulting stock was: cured tighter than may be desirable; With every type of accelerator, however, the o-chlorobenzotrichloride had a powerful activating, effect.

EXAMPLE 3.

The'activating effect of o-chlorobenzotrichloride with a variety of accelerators in GR-S is shown in Table III. GR-S is the name of the butadiene styrene copolymer rubber made in government plants by the copolymeri'zation of approximately 75 parts of butadiene and approx- 75 imately 25 parts of styrene.

Table III Medium processing carbo blac Zinc ox Lead salt of mercaptobenzothiazola 1. Oyclohexylamino-2-thiobenzothiazole Mercaptobcnzothiazole Diphenyl guanidine.

2Mercaptothiazoline Butyraldehyde-aniline condensation product O-Ohlorbenzotrichloride Minutes Stock Cure at Q, R S T U V W X 30 050 750 500 800 275 1,050 550 050 M300 50 1,225 1,500 1,300 1,550 850 1,725 1,100 1,100 30 1,450 1,900 1,550 1,375 1,150 2,150 1,300 1,100 30 2,150 2,725 1,750 3,000 1,100 3,075 1,150 2,550 TB 50 3,050 3,525 3,250 3,300 2, 475 3,225 2,150 2,450 90 3,175 3,525 3,150 3,275 3,100 3,575 2,450 3,050 30 530 575 5 720 500 510 580 E 50 555 540 555 425 510 450 435 510 00 400 455 450 435 555 420 400 550 Heat Build-up 0. 100 68 61 66 61 58 90 7G 1 Goodrich flexometer, is stroke, min.

The stocks containing o-chlorobenzotrichlo- Table V ride are characterized by high tensile strength and low heat build-up. 0 stock Y Z EXAMPLE 4: Smoked Sheets 1. 100 100 Medium Processing Carbon Black 25 Zinc Oxide 5 5 Various chloromethyl aromatic compounds g i were tested as accelerator activators in GR-S in Mircaptobenzothiazole 1 1 the following formula: 0- hlorobenzotrlchlonde 2 Parts GRFS 100 Medium processing carbon black Cur 0 0 Y z Zinc oxide 5 Stock Sulfur 2 0R Lead salt of mercaptobenzothiazole 0.4 m8 Activatcr n 2 50 227 400 150 O l Cured 30 minutes at 298 F. M 15 287 1,450 1,000 g0 33; p 30 1,375 0 0 2, 25 The results of these tests are shown in Table IV. 50 227 1,575 375 TB 15 237 4,050 3,475 g 38; 330 4,550 5 ,3 5 4,5 5 Table IV 50 50 227 81 000 EB 15 237 745 810 30 287 715 790 Activator M500 TB EB 60 287 720 715 ggf g gg ggig ggg fi ff 5 i g; The stock activated With o-chlorobenzotrichlo- 2, 4c-llgichlorobenzotrichloride 1, 250 3, ride in addition to having excellent tensile g ggggggggggggg g- 2 8 510 840 strength also possesses a high degree of safety in 2,4-Dich10robe y c 0 0 900 processing, as shown by the low tensile strength developed on the scorch test, run for minutes 60 at 227 F., as shown in Table V.

It will be seen from this that only the trichlo- While a limited number of trichloromethyl aryl romethyl derivatives are effective accelerator accompounds have been used in the specific examtivators. ples above given to illustrate their efiectiveness as accelerator activators for sulfur vulcanizable EXAMPLE 5 elastomers, it is to be understood that these compounds are given only to illustrate the invention,

It is often desirable to compound a stock with and not as limitations thereon. As further illuslow sulfur content in order to improve the heat tratlng the class of compounds contemplated for aging properties or" the vulcanizate. Frequently, use in the present invention as accelerator actihowever, the use of low sulfur-high accelerator vators, may be mentioned: ratios results in vulcanizates having low tensile strength. By the use of trichlorolnethyl aro- Alpha-trlchloromethyl naphthalene matic compounds as activators, low sulfur stocks p-Bromobenzotrichloride may be obtained that have excellent tensile p-Nitrobenzotrichloride strength. This is shown in Table V. o-Methoxybenzotrichloride The accelerator activators of the present invention may be used with any of the organic accelerators normally used in the sulfur vulcanization of sulfur vulcanizable elastomers such as the aldehyde amine condensation products; guanidines; thiuram sulfides (mono-, diand poly) and the thiazoles, thiazolines and dithiocarbamates, either as such, or. as their esters or salts.

The amount of accelerator activator used will depend on the results which are desired, and will vary in general from 0.1 part to parts per 100 parts of eiastomer. The preferred range is 0.5 to 2 parts of activator. Since the various accelerators are used in the sulfur vulcanization of elastomers for obtaining particular results, the choice of such accelerators Will still depend upon the same factors as ordinarily govern their use in the vulcanization of these elastomers. The accelerator activators of the present invention improve the vulcanization of these elastomers when any of the accelerators are employed, and the amount to be used will depend upon the results which it is desired to obtain. lhese accelerator activators may be used with any of the softeners, peptizing agents, fillers and other types of compounding ingredients commonly used in the rubber industry.

The preferred accelerator activatorsof this class are o-chlorobenzotrichloride, p-chlorobenzotrichloride and 2,4-dichlorobenzotrichloride.

This invention provides an entirely new class of accelerator activators of unusual versatility. They are efiective with all types of accelerators in all kinds of sulfur-vulcanizable elastomers, including natural rubber. By the use of these new accelerator activators, a part of the relatively expensive organic accelerator can be replaced by the very cheap activator. These activators also enable one to obtain vulcanizates of low sulfur stocks having unusually good tensile strength.

The term elastomer is used in this specification in the now generally accepted sense more particularly defined by Fisher in Ind. 81 Eng. Chem, volume 31, No. 8, August 1.939, pages 941-945, and includes natural rubber and synthetic polymers which have rubber-like properties. The expression sulfur vulcanizable elastomer is used to designate those elastomers with which sulfur is normally used as the vulcanizing agent.

We claim:

1. In the process of vulcanizing sulfur vulcanizable elastomers of the group consisting of natural rubber, 1,3-butadiene-styrene co-polymers and 1,3 -butadiene-acrylonitrile co-polymers in each of which co-polymers the l,3'-butarj.iene is present to an extent of from 50% to 98% of the total polymerizable material wherein sulfur is used as the vulcanizing agent together with a vulcanization accelerator, the step which comprises incorporating in the vulcanizable stock,

together with sulfur and a vulcanization accelerator, from 0.1 to 5 parts, per 100 parts of elastomer, of a compound of the group consisting of the trichloromethyl aryl compounds of the benzene and naphthalene series which contain no further substituents than those which carry in the aryl ring a substituent of the groupconsisting of halogen, nitro and methoxy groups.

2. In the process of vulcanizing rubber wherein sulfur is used as the vulcanizing agent together with a vulcanization accelerator, the step which comprises incorporating in the vulcanizable stock, together with sulfur and a vulcanization accelerator, from 0.1 to 5 parts, per parts of rubber, of a compound of the group consisting of the trichloromethyl aryl compounds of the benzene and naphthalene series which contain no further substituents than those which carry in the aryl ring a substituent of the group consisting of halogen, nitro and methoxy groups.

3. In the process of vulcanizing butadienestyrene copolyrner rubber in which the 1,3-butadiene is present to an extent of from 56% to 98% of the total polymerizable material wherein sulfur is used as the vulcanizing agent together with a vulcanization accelerator, the step which comprises incorporating in the vulcanizable stock, together with sulfur and a vulcanization accelerator, from 0.1 to 5 parts, per 100 parts of the rubber, of a compound of the group consisting of the trichloroin thyl aryl compounds of the benzene and naph halene series which contain no further substituents than those which carry in the aryl ring a substituent of the group consisting of halogen, nitro and methoxy 4. In the process of vulcanizing sulfur vulcanisable elastomers of the group consisting of natural rubber, 1,3-butadiene-styrene co-polymers and 1,3-butadiene-acrylonitrile co -polymers in each of which co-polymers the 1,3-butadiene is present to an extent of from 50% to 98% of the total polymerizable material wherein sulfur is used as the vulcanizing agent together with a vulcanization accelerator, the step which comprises incorporating in the vulcanizable stock, together with sulfur and a vulcanization accelerator, from 0.1. to 5 parts, per 106 parts of elastomer, of o-chlorobenzotrichloride.

5. In the process of vulcanizing sulfur vulcanizable elastomers of the group consisting of natural rubber, 1,3-butadiene-styrene co-polymers and 1,3-butadiene-acrylonitrile co-polymers in each of which co -polymers the 1,3-butadiene is present to an extent of from 50% to 98% of the total polymerizabie material wherein sulfur is used as the vulcanizing agent together with a vulcanization accelerator, the step which com-- prises incorporating in the vulcanizable stock, together with sulfur and a vulcanization accelerator, from 0.1 to 5 parts, per 100 parts of elastomer, of p-chlorobenzotrichloride.

6. In the process of vulcanizing sulfur vulcanizable elastomers of the group consisting of natural rubber, 1,3-butadiene-styrene co-polymers and 1,3-butadiene-acrylonitrile co-polymers in each of which co-polymers the LS-butadiene is present to an extent of from 50% to of the total polymerizable material wherein sulfur is used as the vulcanizing agent together with a vulcanization accelerator, the step which comprises incorporating in the vulcanizable stock, together with sulfur and a vulcanizati 1 accelerator, from 0.1 to 5 parts, per 10c par tomer, of 2,4-dichlorobenzotrichloride.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,871,037 Cadwell Aug. 9, 1932 

